1 /* 2 * Copyright (C) 2009 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package android.app.backup; 18 19 import android.os.ParcelFileDescriptor; 20 21 import java.io.FileDescriptor; 22 import java.io.IOException; 23 24 /** 25 * Provides the structured interface through which a {@link BackupAgent} commits 26 * information to the backup data set, via its {@link 27 * BackupAgent#onBackup(ParcelFileDescriptor,BackupDataOutput,ParcelFileDescriptor) 28 * onBackup()} method. Data written for backup is presented 29 * as a set of "entities," key/value pairs in which each binary data record "value" is 30 * named with a string "key." 31 * <p> 32 * To commit a data record to the backup transport, the agent's 33 * {@link BackupAgent#onBackup(ParcelFileDescriptor,BackupDataOutput,ParcelFileDescriptor) 34 * onBackup()} method first writes an "entity header" that supplies the key string for the record 35 * and the total size of the binary value for the record. After the header has been 36 * written, the agent then writes the binary entity value itself. The entity value can 37 * be written in multiple chunks if desired, as long as the total count of bytes written 38 * matches what was supplied to {@link #writeEntityHeader(String, int) writeEntityHeader()}. 39 * <p> 40 * Entity key strings are considered to be unique within a given application's backup 41 * data set. If a backup agent writes a new entity under an existing key string, its value will 42 * replace any previous value in the transport's remote data store. You can remove a record 43 * entirely from the remote data set by writing a new entity header using the 44 * existing record's key, but supplying a negative <code>dataSize</code> parameter. 45 * When you do so, the agent does not need to call {@link #writeEntityData(byte[], int)}. 46 * <h3>Example</h3> 47 * <p> 48 * Here is an example illustrating a way to back up the value of a String variable 49 * called <code>mStringToBackUp</code>: 50 * <pre> 51 * static final String MY_STRING_KEY = "storedstring"; 52 * 53 * public void {@link BackupAgent#onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor) onBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)} 54 * throws IOException { 55 * ... 56 * byte[] stringBytes = mStringToBackUp.getBytes(); 57 * data.writeEntityHeader(MY_STRING_KEY, stringBytes.length); 58 * data.writeEntityData(stringBytes, stringBytes.length); 59 * ... 60 * }</pre> 61 * 62 * @see BackupAgent 63 */ 64 public class BackupDataOutput { 65 int mBackupWriter; 66 67 /** @hide */ 68 public BackupDataOutput(FileDescriptor fd) { 69 if (fd == null) throw new NullPointerException(); 70 mBackupWriter = ctor(fd); 71 if (mBackupWriter == 0) { 72 throw new RuntimeException("Native initialization failed with fd=" + fd); 73 } 74 } 75 76 /** 77 * Mark the beginning of one record in the backup data stream. This must be called before 78 * {@link #writeEntityData}. 79 * @param key A string key that uniquely identifies the data record within the application 80 * @param dataSize The size in bytes of this record's data. Passing a dataSize 81 * of -1 indicates that the record under this key should be deleted. 82 * @return The number of bytes written to the backup stream 83 * @throws IOException if the write failed 84 */ 85 public int writeEntityHeader(String key, int dataSize) throws IOException { 86 int result = writeEntityHeader_native(mBackupWriter, key, dataSize); 87 if (result >= 0) { 88 return result; 89 } else { 90 throw new IOException("result=0x" + Integer.toHexString(result)); 91 } 92 } 93 94 /** 95 * Write a chunk of data under the current entity to the backup transport. 96 * @param data A raw data buffer to send 97 * @param size The number of bytes to be sent in this chunk 98 * @return the number of bytes written 99 * @throws IOException if the write failed 100 */ 101 public int writeEntityData(byte[] data, int size) throws IOException { 102 int result = writeEntityData_native(mBackupWriter, data, size); 103 if (result >= 0) { 104 return result; 105 } else { 106 throw new IOException("result=0x" + Integer.toHexString(result)); 107 } 108 } 109 110 /** @hide */ 111 public void setKeyPrefix(String keyPrefix) { 112 setKeyPrefix_native(mBackupWriter, keyPrefix); 113 } 114 115 /** @hide */ 116 protected void finalize() throws Throwable { 117 try { 118 dtor(mBackupWriter); 119 } finally { 120 super.finalize(); 121 } 122 } 123 124 private native static int ctor(FileDescriptor fd); 125 private native static void dtor(int mBackupWriter); 126 127 private native static int writeEntityHeader_native(int mBackupWriter, String key, int dataSize); 128 private native static int writeEntityData_native(int mBackupWriter, byte[] data, int size); 129 private native static void setKeyPrefix_native(int mBackupWriter, String keyPrefix); 130 } 131 132
